A receptacle with a GFCI circuit therein is intended to provide alternating current (AC) supply voltage from a mains source to electrical outlets and to other load devices connected to the receptacle such as other receptacles, lights or the like, and to disconnect the receptacle and the load devices from the source in the event of ground fault, i.e., excessive current to ground. The excessive current may be caused by a person who comes into contact with the hot wire and ground at the same time. GFCI receptacles include a test button and an indicators, typically either a pop-out button or light, so that the user can test the operation of the receptacle without actually creating excessive ground current. Typically, such devices are designed to trip at about 5 ma.
When properly installed, GFCI outlets perform their tasks well. However, if an outlet is installed by someone not trained to do so, it is possible to install it improperly in various ways so that it appears to be working but actually is not capable of opening the supply to the receptacle in response to ground current. If, for example, a homeowner who is not an electrician buys and installs a GFCI receptacle, it is not unusual for him to connect wires from the AC supply to the terminals intended for connecting additional loads to the device. With that connection, pushing a test button on the outlet causes a trip circuit within the outlet to operate. The usual indicator button, which also performs the function of a reset button, pops out, telling the installer that the trip circuit has worked. However, if the installation is not correct, the trip circuit has not actually disconnected the electrical outlets from the supply and is not capable of doing so.